A study of ultrastructural changes accompanying aging in Drosophila melanogaster is proposed. Particular attention is paid to those changes induced by beta-alanine incorporation into integumentary and supporting structures. The role of beta-alanine in coloring and compacting such structures is also explored with the fungus Morchella esculenta. As a far ranging objective, ultrastructural comparisons are made of juvenile and senescent connective tissues of mammals, with particular attention paid to changes induced by beta-alanine incorporation during aging. Electron microscopic autoradiography is used extensively.